In the field of magnetic recording and/or reproducing apparatus, such as audio tape recorder or a video tape recorder (VTR), for example, the general tendency is towards a higher recording density and a higher quality of recording signals. In keeping with this tendency towards the higher recording density, a so-called metal tape in which powders of metals such as Fe, Co or Ni, or alloys thereof, are used as the magnetic powders, or a so-called vacuum-deposited tape in which a magnetic metal material is directly deposited on a base film by the thin film forming vacuum technique, has been developed and put to practical use in many technical fields.
Prior Art and Problem to be Solved
Meanwhile, if the characteristics of the magnetic recording medium having a predetermined coercive force is to be displayed fully, it is required of the core material for the magnetic head to exhibit a higher saturation magnetic flux density as its magnetic properties or characteristics. In addition, if reproduction is to be achieved with the same magnetic head as that used for recording, it is also required of the core material to exhibit a higher magnetic permeability.
Although the Sendust alloy (Fe--Si--Al, Bs about equal to 10 KG) or a Co-base amorphous alloy has so far been used, it is difficult with the Sendust alloy to increase the film thickness because of the larger inner stress imposed on the film and the difficulty in making a thick film due to the susceptibility of the film to growth of the crystal grains. Also the Sendust alloy has the saturation magnetic flux density Bs of about 10 KG, which however falls short in view of the tendency towards an increasing higher recording density. On the other hand, while the Co-base amorphous alloy has satisfactory magnetic properties and may be fabricated with a high saturation magnetic flux density Bs, it has a drawback that, since it is crystallized at 450.degree. C. or thereabouts, it cannot be glass bonded at elevated temperatures for preparing the magnetic head, such that it is not possible to develop a high enough bonding strength.
Among other soft magnetic materials is iron nitride, which is usually formed into a thin film by ion beam vacuum deposition or sputtering in a nitrogen-containing atomosphere, using iron as the target. However, the soft magnetic thin film of iron nitride has a drawback that the coercive force is markedly increased due to heating upon glass bonding and the magnetic properties thereof are inferior in stability.
In the JP Patent KOKAI 63-299219 (1988), there is disclosed a soft magnetic thin film which is aimed at obtaining the above mentioned drawback and which is represented by the formula Fe.sub.x N.sub.y A.sub.z wherein x, y and z each denote the compositional ratios in atomic percent and A denotes at least one of Si, Al, Ta, B, Mg, Ca, Sr, Ba, Cr, Mn, Zr, Nb, Ti, Mo, V, W, Hf, Ga, Ge and rare earth elements, and wherein the compositional ratios are such that
0.5.ltoreq.y.ltoreq.5.0 PA1 0.5.ltoreq.z.ltoreq.7.5 and PA1 x+y+z=100. PA1 0&lt;b.ltoreq.20 and PA1 0&lt;c.ltoreq.22 PA1 0&lt;b.ltoreq.20 and PA1 0&lt;c.ltoreq.22 PA1 0&lt;b.ltoreq.20 and PA1 0&lt;c.ltoreq.22 PA1 0&lt;b.ltoreq.20 PA1 0&lt;c.ltoreq.22
However, it is not preferred to use the soft magnetic thin film described in the JP Patent KOKAI 63-299219 (1988) in preparing a magnetic head by a process including the heating step, such as a glass bonding step, because its coercive force is inevitably increased on heating.
The above film has also a drawback that, because it does not assure uniaxial anisotropy, its magnetic permeability cannot be increased at higher frequencies.
Also, the crystal materials in general tend to be turned into columnar crystals, during the film depositing process, due to the self-shadowing effect, depending on the film forming conditions, so that voids tend to be formed in the grain boundary region resulting in magnetic discontinuity and inferior soft magnetic properties. These self-shadowing effect becomes particularly outstanding when there is a step-like surface irregularity on the underlayer or substrate as in the case of preparation of the magnetic head, or when a thicker film is to be produced, so that sufficient magnetic properties cannot be obtained.
The soft magnetic thin film disclosed in the above prior art publication is not desirable as the magnetic head core material in view of the above mentioned drawbacks.
It is an object of the present invention to provide a novel soft magnetic thin film, a novel method for preparing a soft magnetic thin film and a novel magnetic head, which are free from the above-mentioned problems of the conventional art.
According to the present invention, the above object may be accomplished by a soft magnetic film, a method for producing the soft magnetic film and a magnetic head, which may be summarized in the following manner.
First Aspect:
There is provided a soft magnetic thin film represented by the compositional formula Fe.sub.a T.sub.b N.sub.c wherein the a, b and c each stand for atomic percent and T stands for at least one of Zr, Hf, Ti, Nb, Ta, V, Mo or W and wherein the composition is in the range of
with the exclusion of the range defined by b.ltoreq.7.5 and c.ltoreq.5. Such compositional range is defined by a line conecting points E, F, G, H, I and J in FIG. 1 (referred to as "EFGHIJ composition" hereinafter).
As will become clear hereinafter, this soft magnetic thin film has a saturation magnetic flux density markedly higher than that of the Sendust alloy or the amorphous soft magnetic alloys and can provide a preferred embodiment with a zero magnetostriction to enable excellent soft magnetic properties such as the low coercive force and high magnetic permeability.
On the other hand, the soft magnetic thin film of the present Aspect has an electrical resistivity as high as that of Sendust and may be subjected to heat treatment in the magnetic field to develop uniaxial anisotropy, the magnitude of which can be controlled depending on the composition of the thin film and the duration of heat treatment to realize the high magnetic permeability at higher frequencies meeting requirements of the intended use and application. The thin film of the present Aspect has superior thermal resistance against the glass bonding since its characteristics are not deteriorated by heat treatment up to 650.degree. C. The thin film of the present Aspect also has high hardness and corrosion resistance and hence a high abrasion resistance, in the all, turning out to be a highly reliable material.
The soft magnetic thin film of the present invention exhibits satisfactory step coverage in film formation since the film material can be formed as an amorphous alloy for preparaing a film and can be subsequently heat-treated so as to be turned into a microcrystalline state. In addition, a mirror surface can be easily developed, while the crystal grains can be inhibited from coarsening (excessive grain growth) without the necessity of resorting to a multilayered structure so that a film of a larger thickness (thick film) may be produced.
Thus the soft magnetic thin film of the present Aspect may be employed as the core material for a magnetic head to cope with the high coercivity magnetic recording medium to realize high quality and bandwidth as well as high recording density.
Second Aspect:
There is provided a method for producing a soft magnetic thin film comprising the steps:
forming an amorphous alloy film of the EFGHIJ composition represented by the compositional formula Fe.sub.a T.sub.b N.sub.c wherein a, b and c each stand for atomic percent and T stands for at least one of Zr, Hf, Ti, Nb, Ta, V, Mo or W and wherein the composition is in the range of
with the exclusion of the ranges of b.ltoreq.7.5 and c.ltoreq.5, and
crystallizing the resultant amorphous alloy film by heat treatment.
Although the amorphous alloy film of the above composition exhibits satisfactory step coverage when formed on a substrate having step differences, it fails to exhibit satisfactory soft magnetic properties. The present inventors have found that a thin film exhibiting satisfactory soft magnetic may be obtained by crystallizing the amorphous alloy film by heat treatment to a microcrystalline state, and that a soft magnetic thin film exhibiting uniaxial anisotropy may be obtained when the heat treatment is carried out in a magnetic field. These findings have led to completion of the present invention. (Note here, the term "crystallize" denotes to provide a microcrystalline state.)
As will become clear hereinafter, the soft magnetic thin film produced by the method of the present invention has a saturation magnetic flux density markedly higher than that of the Sendust alloy or the amorphous soft magnetic alloy and can provide a preferred embodiment with a zero magnetostriction to realize excellent soft magnetic properties such as the low coercive force and high magnetic permeability.
On the other hand, the soft magnetic thin film of the present invention has an electrical resistivity as high as that of Sendust and may be subjected to heat treatment in the magnetic field to develop uniaxial anisotropy, the magnitude of which can be controlled depending on the composition of the thin film and the duration of heat treatment to realize the high magnetic permeability at higher frequencies meeting requirements of the intended use and application. The thin film of the present invention has superior thermal resistance against the glass bonding since its characteristics are not deteriorated by heat treatment up to 650.degree. C. Thus the resultant thin film of the present Aspect has the same advantages as those mentioned in the first Aspect.
The soft magnetic thin film of the present Aspect exhibits satisfactory step coverage in film formation since the film material can be formed as amorphous alloy for preparaing a film and can be subsequently heat-treated so as to be turned into the microcrystalline state. In addition, a mirror surface can be easily developed, while the crystal grains can be inhibited from becoming coarse without the necessity of resorting to a multilayered structure so that a film of a larger thickness may be produced. (These advantages are the same as mentioned in the first Aspect).
Thus the soft magnetic thin film produced by the method of the present Aspect may be employed as the core material for a magnetic head to cope with the high coercivity magnetic recording medium to realize high quality and bandwidth as well as high recording density as is the case with the first Aspect.
Third Aspect:
There is provided a composite magnetic head comporsing
a magnetic head core which includes end faces opposing each other and a recess set back from each of said end faces, and a soft magnetic layer exposed to outside provided on each of said end faces, each of said soft magnetic layers having the EFGHIJ composition Fe.sub.a T.sub.b N.sub.c.
Fourth Aspect:
There is provided a thin film magnetic head comprising:
a substrate,
a lower soft magnetic layer, an insulating layer, a coil conductor layer and an upper soft magnetic layer which are provided in this order on the substrate, and
a magnetic gap layer which extends to a surface of the magnetic head directed to the recording medium, and which is provided between the lower soft magnetic layer and the upper soft magnetic layer,
wherein each of the soft magnetic layers has the EFGHIJ composition Fe.sub.a T.sub.b N.sub.c.
As will become clear hereinafter, the soft magnetic thin film of the magnetic head according to the present Aspect has a saturation magnetic flux density markedly higher than that of the Sendust alloy or the amorphous soft magnetic alloy and can provide a preferred embodiment of a zero magnetostriction, to realize excellent soft magnetic properties such as the low coercive force and high magnetic permeability.
This soft magnetic thin film has the same advantageous properties as mentioned in the previous Aspects.
Thus the magnetic head of the present Aspect may be employed as a magnetic head to cope with the high coercivity magnetic recording medium to realize high quality and bandwidth as well as high recording density.
Fifth Aspect:
There is provided a composite magnetic head comprising:
a ferrite core including end faces opposing each other,
a recess receded from each of said end faces,
soft magnetic layers provided between said end faces of said ferrite core and defining a gap, and
a diffusion preventing layer formed of SiO.sub.2 and provided at an interface between said core and the soft magnetic layer,
wherein each of said soft magnetic layers has the EFGHIJ composition Fe.sub.a T.sub.b N.sub.c, particularly T is Zr (i.e., Fe.sub.a Zr.sub.b N.sub.c).
Sixth Aspect:
There is provided a thin film magnetic head comprising:
a ferrite core including end faces opposing each other,
a recess receded from each of said end faces,
soft magnetic layers provided between said end faces of said ferrite core and defining a gap, and
a diffusion preventing layer formed of SiO.sub.2 and provided at an interface between said core and the soft magnetic layer,
wherein each of the soft magnetic layers is represented by the formula Fe.sub.a X.sub.b N.sub.c, where a, b and c each denote the compositional ratios in atomic percent, and X denotes at least one of Hf, Ti, Nb, Ta, V, Mo and W and the composition range is such that
with the exclusion of the case in which b.ltoreq.7.5 and c.ltoreq.5. (This composition is the case where T=X in the EFGHIJ composition Fe.sub.a T.sub.b N.sub.c.)
The composite magnetic head having the diffusion preventing layer according to the 5th and 6th Aspects includes a ferrite core having each other opposing end faces and recesses receded from these end faces, soft magnetic layers of the above mentioned specified compositons which are provided between the opposing end faces of the core for defining a gap, and an diffusion preventive SiO.sub.2 layer provided at the interface between the core and the soft magnetic layer, so that it becomes possible to prevent the formation and growth of a diffusion layer with deteriorated magnetic properties between the ferrite core and the soft magnetic layers of the above mentioned specified compositions. Thus it is possible with the composite magnetic head of the present invention to suppress periodic fluctuations (so called beat) of the frequency characteristics of the reproduced signal during reproduciton to 1 dB or less. It is also possible to make use of the soft magnetic thin film of the above mentioned specified composition, which is freed of the inconveniences of the prior art soft magnetic thin film, as one of the constituent material of the composite magnetic head.
The present inventors arrived at a soft magnetic thin film which is freed of the previously mentioned disadvantages of the prior art soft magnetic thin film, and which is represented by the compositional formula Fe.sub.a Zr.sub.b N.sub.c or Fe.sub.a X.sub.b N.sub.c, wherein a, b and c each denote atomic percent and x denotes at least one of Hf, Ti, Nb, Ta, V, Mo or W, and the compositional ranges are such that
with the exclusion of b.ltoreq.7.5 and c.ltoreq.5 (generally, Fe.sub.a B.sub.b N.sub.c compositon).
However, it has been found that a composite magnetic head utilizing the above mentioned soft magnetic thin film suffers from periodic fluctuations (beat) of frequency characteristics of the reproduced signals during reproduction and hence is insufficient as the magnetic head. The term "composite magnetic head" used herein means a magnetic head having a magnetic head core having each other opposing end faces and recesses receded from said end faces, soft magnetic layers exposed to at least said end faces and defining a gap, and glasses filling said recesses. It has also been found that the above mentioned periodic fluctuations are observed when the ferrite is used as the magnetic head core but are not observed when the nonmagnetic material is used as the magnetic head core.
The present inventors have now found following facts:
(i) a diffusion layer with markedly deteriorated magnetic properties is formed at an interface between the ferrite core and the soft magnetic layer of the above mentioned specific composition as a result of inevitable heating at the time of preparing the composite magnetic head, such as during or after formation of the soft magnetic layer of the specified composition on the ferrite core surface:
(ii) this diffusion layer is formed substantially parallel to the gap and hence acts as a pseudo-gap to affect the reproduced output of the head, such as by the above mentioned periodic fluctuations, and
(iii) formation of such diffusion layer may be prevented from occurring by providing an SiO.sub.2 diffusion preventive layer on the surface of the ferrite core on which the soft magnetic layers of the above mentioned compositon are to be formed. These findings have led to completion of the present invention.
Meanwhile, it is described in the JP Patent KOKAI Publication 63-298806 and 1-100714 to provide a thin film of nonmagnetic nitride film or a thin film of an oxide of Si or the like, respectively, at the interface between the magnetic metal thin film and the magnetic oxide material constituting the core of the composite magnetic head to suppress reactions between the magnetic oxide material and the magnetic metal thin film to prevent formation of the pseudo-gap.
However, there is no teaching in these KOKAI Publications as to the problem which has been newly found by the present inventors and which occurs when the soft magnetic thin film of the aforementioned composition found by the present inventors is used in the composite magnetic head.
The composite magnetic head of the present Aspect includes a ferrite core having the opposing end faces and the recesses receded from said end faces, soft magnetic layers of the above mentioned composition provided between the opposing end faces of the core for defining the gap, and the diffusion preventive SiO.sub.2 layer provided at the interface between the ferrite core and the soft magnetic layer.
It is possible in this manner to prevent the formation and growth of the diffusion layer of deteriorated magnetic properties between the ferrite core and the soft magnetic layer of the above mentioned composition due to heating which inevitably occurs in the course of the preparation of the composite magnetic head of the present invention. In the following, the description will be made on the case where the soft magnetic layer is an Fe--Zr--N soft magnetic layer having the above composition, but the same applies for the Fe.sub.a T.sub.b N.sub.c system.
For example, the Fe--Zr--N soft magnetic layer of the above composition is formed in general by heat-treating a non-soft-magnetic Fe--Zr--N amorphous alloy film at, e.g., 550.degree. C. However, when the Fe--Zr--N amorphous alloy film is directly formed on the ferrite core surface and subjected to heat treatment, the Fe--Zr--N amorphous alloy film is changed into the Fe--Zr--N soft magnetic layer of the above composition, while a diffused layer with deteriorated magnetic properties is formed and caused to grow at the interface between the ferrite core and the Fe--Zr--N soft magnetic layer.
In contrast, when preparing the composite magnetic head of the present Aspect, the diffusion preventive SiO.sub.2 layers are provided at the interface of the Fe--Zr--N amorphous alloy film to prevent the formation of the diffusion layer with deteriorated magnetic properties. In producing a ferrite core composite magnetic head, a set of multilayerd composite magnetic head halves, in each of which a soft magnetic layer and a gap layer are sequentially formed on the opposing end faces and recesses receded from said end faces, are abutted to each other in a predetermined direction, and fused glass is filled and allowed to cool in the recesses of the ferrite core halves. However, when the Fe--Zr--N soft magnetic layers of the above composition are directly formed on the ferrite core halves to produce the composite magnetic head in accordance with the above mentioned method, the diffused layer with deteriorated magnetic properties is formed and allowed to grow at the interface between the ferrite core half and the Fe--Zr--N soft magnetic layer of the above composition.
In the above mentioned method for preparing the inventive composite magnetic head of the 5th or 6th Aspect, distortion or strain of the multi-layered composite magnetic head halves may be relieved by heating. In preparing the composite magnetic head of the Sixth Aspect, since the diffusion preventive SiO.sub.2 layers are provided at the interface between the ferrite core halves of the multi-layered composite magnetic head and the Fe--Zr--N soft magnetic layers of the above composition, distortion or strain of the composite magnetic head halves may be relieved by heating without allowing the formation of the diffusion layer with deteriorated magnetic properties. FIGS. 23 and 24 exhibit the effect of the diffusion preventive SiO.sub.2 layer which will be discussed in detail later.